The reviewers of the A1 application considered the Core essential for the successful accomplishment of all the projects in the Program. Discrepancies between the budget and the grant text have been corrected in the current revision. The letter from Ms. Karin Eastham, Vice President and Chief Operating Officer of the Burnham Institute, is enclosed at the end of section II and also in the Appendix. This letter states that the Burnham Institute will provide, as part of its commitment to this Program, two rigs for electrophysiological recording from slices and cell cultures. It is also now clearly stated that both Research Associates, Dr. Hadieh Badie-Mahdavi and Dr. Barbara Fredette, will contribute their expertise to the work in Core A starting in year 1. Their effort has been reduced to 50%, as recommended by the reviewers. This also reflects decreased needs due to elimination of the previous Project 1. Dr. Ranscht's effort, on the other hand, has been increased to 15% due to her ability to dedicate increased effort to the preparation of mixed neuron-glia cultures and also due to the need for her consultation to evaluate the effects of heparan sulfate proteoglycans and NG2 at the nodes of Ranvier, as recommended by the reviewers. The revised portions of the application are indicated with a line on the left margin. The overall editorial modifications introduced to unify the style of the application are not marked